This invention relates to a coarse-fine focusing gear for microscopes with automatic focusing by means of a motor drive acting on the focusing gear which is preferably controlled by signals that vary with image contrast.
An adjustment mechanism with single-knob control for coarse-fine focusing adjustment is disclosed in Leitz publication "Schul- und Kursmikroskop HM," list 512 -63a. The axle of the mechanism is permanently connected to the control knob, a worm screw or helix is rotatably mounted on the axle and allowance is made for sliding of the worm screw in an axial direction. The worm screw is rotated by engagement between follower pins inserted on the axle and on one face of the worm screw. As long as the follower pins are not in meshing engagement, a mechanism comprising an inclined plane and a sphere and coupled to the axle causes the worm screw to move in axial direction. The worm meshes with a worm gear pinion which causes the specimen to be adjusted via a rack-and-pinion gear. Both the rotation of the worm screw and its axial movement cause the worm gear to rotate. Due to the varying pitch ratios they cause in the former case, a coarse focusing adjustment and, in the latter case, a fine focusing adjustment. The fine focusing range is delimited by the stop of the follower pins.
An adjustment mechanism for coarse-fine motion is disclosed in the Leitz publication "Das Planetengetriebe des Orthoplan, Ein Praezisionsantrieb im Mikroskopbau," loose leaf to list 512 - 82b, wherein the fine focusing motion is employed over the whole adjustment range of the gear independently of the coarse focusing motion. The coarse-fine focusing gears are coupled via a common planetary gear and act on the same terminal gear wheel for vertical motion of the specimen stage or mount. Power is transferred by means of separate coaxial control knobs.
Automatic focusing by means of a motor drive controlled by signals that vary with image contrast is known from West German Petty Pat. No. 7,219, 226, wherein the adjustment device for raising and lowering the specimen stage or mount is illustrated schematically.